Double-Walled Round and Oval HVAC Ductwork Systems Using Phenolic Insulation

ABSTRACT

The present invention involves the preparation and manufacture of phenolic insulation boards for use in double-walled ductwork systems. The preparation of the phenolic insulation board, having a first and second surface each having a foil coating, includes the cutting or grooving of V-grooves into the first surface of the phenolic insulation and first foil coating. This grooving process creates a continuous piece of phenolic insulation having trapezoidal shapes along the second surface and second foil coating. The prepared phenolic insulation board can then be wrapped around an inner sheet metal duct and then covered with an outer shell. Alternatively, the prepared phenolic insulation board can be inserted between an inner duct and outer shell. Both result in a double-walled phenolic insulation ductwork systems.

TECHNICAL FIELD

The present invention relates to the field of heating, ventilation, and air conditioning (“HVAC”) systems and insulated of ductwork. Particularly, the present invention relates to the manufacture, installation, and use of double-walled round or oval ductwork systems using phenolic insulation situated between an inner duct and outer shell.

BACKGROUND

Double-walled metal ducts have been used extensively for over fifty years in the HVAC industry, but have utilized low-density insulation media such as fiberglass that can be readily compressed or formed around an inner duct. Phenolic board insulation, such as Kingspan® KoolDuct®, has desirable properties as an insulator, but the higher density of the phenolic material, versus traditional fiberglass insulations, prevents it from being compressed and rolled around the exterior surface of an inner duct. The properties of the phenolic board insulations make it particularly desirable for ductwork outside a building's envelope. The phenolic board insulations are a closed-cell material, so it resists retaining moisture like glass or mineral fibers. The phenolic board insulations have excellent fire/smoke ratings, which is an important consideration for building construction and particularly ductwork. Phenolic insulation “R-values” (insulating material's resistance to conductive heat flow is measured or rated in terms of its thermal resistance or R-value—the higher the R-value, the greater the insulating effectiveness) are more than 50% greater than R-values for fiberglass and elastomeric insulations of the same thickness. Phenolic board insulation materials have previously been used in some ductwork insulations, but these prior products are rectangular in shape. The prior products require slabs of the phenolic board to be assembled into a rectangular profile, then overlaid with a metal lagging material. But this design and process is not desirable for a number of reasons. First is the excessive use of materials from forming a rectangular shape around a rectangular shaped duct work. The second issue are the seams created from overlapping corners of in forming the rectangular shape. Another issue caused by these prior designs is the size and inability to optimally route the ductwork that is capable of carrying the desired amount of airflow for a given installation. Another known issue with these prior design is that they are not suited or potentially illegal for rooftop installations, as rooftop ductwork should preferably use a rounded profile when possible. Rounded ductwork has about 40% of the design wind force that rectangular ductwork must meet to satisfy building and safety regulations and ordinances. The present invention is needed to minimize excessive waste of insulation materials, allow for faster and more efficient installation of ductwork that better insulates than prior products, and because of ever increasing wind design regulations that are mandated in building codes and ordinances across the United States.

There is no rooftop ductwork product using phenolic insulation currently made in a round or oval profile. Current products using phenolic insulation require fabrication of rectangular ducts which are installed by a sheet metal contractor, after installation of the rectangular ductwork the insulation is installed around the exterior of the previously installed ductwork and lagged by an insulation contractor. This process is not desirable as it necessitates a three-step process, creates excessive use of materials and labor, and restricts the placement and location of ductwork so as to allow sufficient space for the later installation of the insulation.

Engineers, architects, and building owners have been looking for alternatives to mineral fiber insulations in ductwork outside the building envelope for several years. Common problems with prior systems and products are moisture wicking/retention in the fibrous insulation used and the resultant problems of water damage within the building and potential mold/bacteria problems.

Prior attempts used to overcome the problems outlined above, included the use of elastomeric insulation, which is considered “closed cell” so moisture retention does not present an issue. However, elastomeric insulation is expensive, heavy, and not easily formed into a round or oval profile for use in ductwork. Additionally, when used in sufficient thicknesses to obtain an R-8 or R-12 rating the elastomeric insulation can exceed allowable flame spread ratings and/or smoke developed indices. The next system and method attempted included the process of injecting an insulating foam between an inner sheet metal duct situated inside an outer sheet metal shell forming a double-walled duct. This process was found to be both expensive and messy.

There is a strong need for a system and method of assembly, such as the present invention described herein, which provides an insulated round or oval shaped double-walled duct that can be assembled in a one-step process while being cost effective, closed cell, have an R-value of 8 or more, and a 25/50 flame spread/smoke developed rating.

SUMMARY OF INVENTION

The present invention involves routing V-grooves or trapezoidal segments into a phenolic board so that it can be rolled into a polygon approximating a round or flat oval form, after which it can be inserted between an inner sheet metal duct and an outer sheet metal shell forming a “double-walled” sheet metal duct in much the same way as traditional fiberglass media. This particular routing process is necessary, rather than simply creating straight cuts, because the phenolic insulation board is found to be too dense to compress the segment edges together when formed into a round or oval shape. Phenolic insulation board is commonly covered on both a front and rear surface with a foil coating. In routing the phenolic insulation board, the foil coating on the front side is cut into while the foil coating on the rear surface remains at the apex of the V-grooves or trapezoidal segments. The resulting profile is a series of trapezoids joined by a continuous foil surface. The angle of the V-groove is such that when the insulation board is “rolled” to round or flat oval, the V-grooves are closed so that no thermal breaks occur in the resulting cylinder. In other words, the foil coating surface of the phenolic board into which the cuts or V-grooves are made abuts an exterior surface of the inner sheet metal duct and the continuous, uncut foil coating abuts an inner surface of the outer metal sheet metal shell. By varying the number, spacing, or angle of the cuts, V-grooves, round or oval cylinders of different diameters can be formed for insertion between different sizes of inner sheet metal duct and outer sheet metal shells. It should be appreciated that the spacing, angle, and quantity of each V-groove or trapezoidal segment must be precisely determined for the size and thickness of the phenolic board and the size of the inner sheet metal duct and outer sheet metal shell between which the prepared phenolic board is to be inserted so that the prepared phenolic board can be rolled into a cylindrical shape without causing compression of the segment edges while minimizing any gaps between the segments when rolled around the inner sheet metal duct.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a depiction of an isometric view of a straight section of the double-walled ductwork as described herein.

FIG. 2 is a depiction of an isometric view of a double-walled ductwork including angled end portions as described herein.

FIG. 3 is a depiction of isometric view of a T-intersection embodying the double-walled ductwork as described herein.

FIG. 4 is a profile depiction of the prepared, V-grooved phenolic insulation board after being rolled, as described herein.

FIG. 5 is a profile depiction of the prepared, V-grooved phenolic insulation board.

FIG. 6 is an isometric depiction of a plurality of prepared, V-grooved phenolic insulation boards, as described herein.

FIG. 7 is a table detailing various physical properties and qualities of a phenolic insulation board.

DESCRIPTION OF EMBODIMENTS

This invention includes a method for producing a double-walled HVAC ductwork system with traditional double-walled duct characteristics, but utilizing a phenolic insulation board as an interstitial insulation media in lieu of traditional mineral glass products. The presently described double-walled ductwork systems can be installed on the jobsite in a single operation and by the HVAC contractor. This differs from attempting to use phenolic insulation board to cover an HVAC ductwork, then lag the exterior—a process that involves both the HVAC installer and an insulation installer. Also, double-walled ductwork products are traditionally made with an outer sheet metal shell functioning as both the pressure containment shell and the primary protective layer (inner sheet metal ducts are often perforated metal for sound absorption). Existing rectangular phenolic insulation ductwork systems utilize a phenolic insulation board itself as pressure containment. The phenolic insulation board is usually covered with a foil surface or scrim on a front and rear surface of the phenolic insulation board, so a secondary process must be used to repair any breaks or tears on the foil surface abutting the exterior surface of the inner sheet metal duct so as to isolate interaction between the phenolic insulation and the airstream. A tertiary process is needed to form a more durable layer on an outer sheet metal shell exterior, usually a metal lagging.

The fabrication steps of this invention are as follows: (1) an inner sheet metal duct and outer sheet metal shell are manufactured and prepared. (2) A section of phenolic insulation board is “grooved” using a router or cutting blade by cutting into one of the foil coatings formed on a first surface of the phenolic insulation board. It should be appreciated that the V-grooves can be varied and do not need to be parallel to each other, but can be angled or vary their direction and spacing to allow various shapes to be formed when the grooved phenolic board is wrapped or rolled. By way of example, one or more V-grooves are formed on the phenolic insulation board are triangular with an apex at the second foil coating or scrim layer on a second surface of the phenolic insulation board. The angle and frequency of the V-grooves or cuts are calculated to produce a substantially round or oval polygon shape, when the first surface of the phenolic insulation is wrapped around the inner sheet metal duct, so that the cut, first surface abuts the exterior surface of the inner sheet metal duct. When “rolled” the V-grooves should fill the annular space between the inner sheet metal duct and the outer sheet metal shell while minimizing voids between segments and the inner sheet metal duct and outer sheet metal shell. (3) The grooved phenolic insulation board is then wrapped around the inner sheet metal duct, then the resulting assembly of the wrapped inner sheet metal duct is then inserted into the outer metal shell. This process forms a complete double-walled phenolic insulation ductwork, which can then be installed in a single step by a single installer.

FIG. 1 is a depiction of an embodiment of a straight pipe double-walled ductwork made using the methods described herein. The ductwork 100 comprises end joints 102 to allow joining the ductwork to other pieces of ductwork or other connections, such as an HVAC intake or outflow. The ductwork 100 further comprises an exterior metallic shell or duct 120, most commonly made from sheet metal. The grooved phenolic insulation board 106 includes a foil coating or scrim 104 which abuts an interior surface of the exterior metallic shell or duct 120. The grooved phenolic insulation board also includes a foil coating or scrim 108 that abuts an exterior surface of the interior metallic duct 110. The grooved phenolic insulation board 106 is situated between the metallic shell or duct 120 and an interior duct 110, so as to minimize voids between the grooved segments of the phenolic insulation board. The grooved phenolic insulation board 106 includes a plurality of segments 118 formed by creating V-grooves 115, each segment 118 includes a first surface 116 and a second surface 117, such when the grooved phenolic insulation board is wrapped or installed around the interior duct 110 a first surface 116 of a first segment 118 abuts a second surface 117 of an adjacent second segment 118. It should be appreciated that the ductwork pieces can be varied in size, shape, dimensions to allow for varied applications, connections, and fittings for ductwork installation, while still being within the scope of this disclosure and claims.

FIG. 2 is an embodiment of a double-walled ductwork 200, as described and claimed herein, which includes angled joints. This embodiment is prepared using the same steps as described above for each joint. As depicted in FIG. 2 , this embodiment comprises three individual straight joints 220, 222, 224 joined by weld joints 230. It is to be understood that any configuration of angles, tapers, and sizes can be accommodated and prepared using the steps described herein. The ductwork 200 comprises end joints 202 to allow joining the ductwork to other pieces of ductwork or other connections, such as an HVAC intake or outflow. The ductwork 200 further comprises an exterior metallic shell or duct 220, 222, 224, most commonly made from sheet metal. The grooved phenolic insulation board 206 includes a foil coating or scrim 204 which abuts an interior surface of the exterior metallic shell or duct 220, 222, 224. The grooved phenolic insulation board also includes a foil coating or scrim 208 that abuts an exterior surface of the interior metallic duct 210. The grooved phenolic insulation board 206 is situated between the metallic shell or duct 220, 222, 224 and an interior duct 210, so as to minimize voids between the grooved segments of the phenolic insulation board. The grooved phenolic insulation board 206 includes a plurality of segments 218 formed by creating V-grooves 215, each segment 218 includes a first surface 216 and a second surface 217, such when the grooved phenolic insulation board is wrapped or installed around the interior duct 210 a first surface 216 of a first segment 218 abuts a second surface 217 of an adjacent second segment 218.

FIG. 3 is another embodiment that can be prepared using the steps described and claimed herein. As depicted in FIG. 3 , the T-intersection embodiment comprises two individual straight joints 320, 322 joined by weld joint 330. It is to be understood that any configuration of angles, tapers, and sizes can be accommodated and prepared using the steps described herein. The ductwork 300 comprises end joints 302 to allow joining the ductwork to other pieces of ductwork or other connections, such as an HVAC intake or outflow. The ductwork 300 further comprises an exterior metallic shell or duct 320, 322 most commonly made from sheet metal. The grooved phenolic insulation board 306 includes a foil coating or scrim 304 which abuts an interior surface of the exterior metallic shell or duct 320, 322. The grooved phenolic insulation board also includes a foil coating or scrim 308 that abuts an exterior surface of the interior metallic duct 310. The grooved phenolic insulation board 306 is situated between the metallic shell or duct 320, 322 and an interior duct 310, so as to minimize voids between the grooved segments of the phenolic insulation board. The grooved phenolic insulation board 306 includes a plurality of segments 318 formed by creating V-grooves 315, each segment 318 includes a first surface 316 and a second surface 317, such when the grooved phenolic insulation board is wrapped or installed around the interior duct 310 a first surface 316 of a first segment 318 abuts a second surface 317 of an adjacent second segment 318.

FIGS. 4, 5, and 6 show various depictions of a prepared, V-grooved phenolic board as described and claimed in herein. The phenolic board 106 includes a first foil coating or scrim 402 and a second foil coating or scrim 404. The grooved phenolic insulation board 106 is prepared by routing or cutting V-grooves 415 into the board 106 through the first foil coating or scrim 402 to form a plurality of segments 418. Preferably, the second foil coating or scrim 404 should not be cut into or disturbed during the routing and cutting of the V-grooves, so as to allow the phenolic insulation board to maintain itself as a single piece. Although, maintaining the phenolic insulation board as single piece is not necessary to achieve the improvements and benefits described herein. The plurality of segments 418 formed by the V-grooves 415 each include a joint 406, a first surface 416 and a second surface 417, such that when the grooved phenolic insulation board 106 is wrapped or installed around an interior duct a first surface 416 of a first segment 418 abuts a second surface 417 of an adjacent second segment 418. The joints 406 comprise a portion of phenolic insulation board material, the second foil coating or scrim 404, or both. The width and angle 410 and/or depth 412 of the routed or cut V-grooves 415 and joints 406 can be varied, spaced, and calculated to allow the phenolic board to be wrapped or situated around a round or oval duct so as to minimize the space or voids between segments 418 when the phenolic insulation board is installed in the ductwork. It should be appreciated that the minimization of space or voids between segments of the phenolic insulation board is important and an improvement over prior systems as this method provides improvements in insulation ductwork as described herein. By varying the number, spacing, or angle of the V-grooves round, oval, or tapered cylinders of different diameters, shapes, and sizes can be formed for insertion between different sizes of inner sheet metal duct and outer sheet metal shells. It should be appreciated that the spacing, angle, and quantity of each V-groove or trapezoidal segment must be precisely determined for the size and thickness of the phenolic board and the size of the inner sheet metal duct and outer sheet metal shell between which the prepared phenolic board is to be inserted so that the prepared phenolic board can be rolled into a cylindrical shape without causing compression of the segment edges while minimizing any gaps between the segments when rolled around the inner sheet metal duct.

This process and system produces a single finished apparatus that can be assembled with traditional external HVAC joining methods. As a “double-walled” ductwork, the phenolic insulation board is isolated from both the airstream within the inner sheet metal duct and the elements outside the assembly. With regards to the Table depicted in FIG. 7 , the phenolic insulation board, when compared to traditional mineral fiber insulations, is closed cell and resists retention of moisture, has an inherent vapor barrier via the foil coating/scrim coating, and has greater thermal properties. When compared to elastomeric insulations, the phenolic insulation board has greater thermal properties and significantly better flame spread/smoke developed ratings. For all profiles, when compared to mineral fiber and elastomeric products, the greater rigidity of the phenolic insulation board allows larger spans of ductwork to be manufactured without the need to reinforce the inner sheet metal duct against sagging.

Alternatively, an outer sheet metal shell can be wrapped and then sealed, clamped or otherwise joined around the phenolic insulation board and inner sheet metal duct assembly instead of the “stuffing” method described above.

Alternatively, the phenolic insulation board can be initially formed or machined as a cylinder for inserting into the annular space between the inner sheet metal duct and outer sheet metal shell. This would eliminate the need for grooving, as described above. It should be appreciated that different transverse ductwork connections can be used in place of those described in the preferred embodiments herein, such as those depicted in FIGS. 1, 2, and 3 including, but not limited to, tapered or conical-cylindrical ductwork pieces.

It should be appreciated that other rigid insulation products, such as polyisocyanurate, could also be used by the above-described grooving and insertion methods. Alternatively, the system and methods described herein could also be completed using high density foams as the insulating material in the double-walled duct. It should be appreciated that the fabrication method described herein could be applied to other types of ductwork, such as grease ducts, boiler ducts, fire-rated chimneys or the like. 

1. A double-walled ductwork segment comprising: a first cylindrical sleeve comprising an interior diameter; a second cylindrical sleeve comprising an outer diameter smaller than the interior diameter of the first cylindrical sleeve; and an insulation layer situated between the first cylindrical sleeve and the second cylindrical sleeve, the insulation layer comprising a first surface, a second surface, and a closed-cell membrane, wherein the insulation layer further comprises a plurality of trapezoidal segments comprising channels formed on the first surface and in the closed-cell membrane, wherein each trapezoidal segment comprises a first surface and a second surface, wherein when the insulation layer is situated between the first cylindrical sleeve and second cylindrical sleeve the first surface of a first trapezoidal segment abuts the second surface of an adjoining trapezoidal segment.
 2. The double-walled ductwork segment of claim 1, wherein the first cylindrical sleeve is circular.
 3. The double-walled ductwork segment of claim 2, wherein the second cylindrical sleeve is circular.
 4. The double-walled ductwork segment of claim 1, wherein the first cylindrical sleeve is oval.
 5. The double-walled ductwork segment of claim 4, wherein the second cylindrical sleeve is oval.
 6. The double-walled ductwork segment of claim 1, wherein the insulation layer comprises phenolic insulation board.
 7. The double-walled ductwork segment of claim 6, wherein the first surface of the insulation layer comprises a first foil coating.
 8. The double-walled ductwork segment of claim 7, wherein the first surface of the insulation layer comprises a second foil coating.
 9. The double-walled ductwork segment of claim 8, wherein the trapezoidal segments are shaped and angled to minimize voids between the first and second surfaces of the plurality of trapezoidal segments in the insulation layer when the insulation layer is wrapped around an exterior surface of the second cylindrical sleeve.
 10. An apparatus comprising: a first circular tube comprising an interior diameter; a second circular tube comprising an outer diameter smaller than the interior diameter of the first circular tube; an insulation layer situated between the first circular tube and second circular tube, wherein the insulation layer comprises a first surface, a second surface, and a phenolic insulation board.
 11. The apparatus of claim 10, wherein the insulation layer further comprises a plurality of v-shaped grooves formed on the first surface and in the phenolic insulation board, wherein each v-shaped groove comprises a first surface and a second surface.
 12. The apparatus of claim 11, wherein when the insulation layer is situated between the first circular tube and the second circular tube the first surface of a first v-shaped groove of the plurality of v-shaped grooves abuts a second surface of an adjacent second v-shaped groove.
 13. The apparatus of claim 12, wherein the first surface of the insulation layer is a first foil coating.
 14. The apparatus of claim 13, wherein the second surface of the insulation layer is a second foil coating.
 15. The apparatus of claim 12, wherein the first circular tube and second circular tube comprise sheet metal.
 16. The apparatus of claim 14, wherein the first circular tube and second circular tube comprise sheet metal.
 17. The apparatus of claim 16 wherein the v-shaped grooves are shaped and angled to minimize voids between the first and second surfaces of the plurality of v-shaped grooves in the insulation material when the insulation material is wrapped around the exterior surface of the second circular tube.
 18. A method of preparing a double-walled ductwork segment comprising: routing a plurality of v-shaped grooves into an insulation material, wherein each v-shaped groove has a first surface and a second surface; wherein the plurality of v-shaped grooves are spaced and angled to allow the first surface of a first v-shaped groove to abut the second surface of an adjacent v-shaped groove when the insulation material is wrapped around an exterior surface of an interior duct; and insertion of the insulation material wrapped interior duct into an annular space of an exterior duct.
 19. The method of claim 18 wherein the insulation material comprises phenolic insulation board further comprising a first surface, a second surface, and a close-cell membrane situated between the first and second surfaces.
 20. The method of claim 19 wherein the v-shaped grooves are shaped and angled to minimize voids between the first and second surfaces of the plurality of v-shaped grooves in the insulation material. 